(Objective-C) Validate a JWS Using ECDSA P-256 SHA-256

Validates a JSON Web Signature (JWS) that uses ECDSA P-256 SHA-256

Note: This example requires Chilkat v11.0.0 or greater.

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#import <CkoStringBuilder.h>
#import <CkoPublicKey.h>
#import <CkoJws.h>
#import <CkoJsonObject.h>

BOOL success = NO;

// This requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// This example takes a JSON signature in compact serialization format,
// and uses an ECDSA public key to validate and recover the protected header and payload.

// We only need a public key for signature validation.  This is the ECDSA public key
// that is used:

//      {"kty":"EC", 
//       "crv":"P-256", 
//       "x":"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU", 
//       "y":"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0" 
//      } 

CkoStringBuilder *sbPubKey = [[CkoStringBuilder alloc] init];
[sbPubKey Append: @"{\"kty\":\"EC\","];
[sbPubKey Append: @"\"crv\":\"P-256\","];
[sbPubKey Append: @"\"x\":\"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU\","];
[sbPubKey Append: @"\"y\":\"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0\""];
[sbPubKey Append: @"}"];

CkoPublicKey *pubKey = [[CkoPublicKey alloc] init];
success = [pubKey LoadFromString: [sbPubKey GetAsString]];
if (success == NO) {
    NSLog(@"%@",pubKey.LastErrorText);
    return;
}

CkoJws *jws = [[CkoJws alloc] init];

// Set the ECC public key:
int signatureIndex = 0;
[jws SetPublicKey: [NSNumber numberWithInt: signatureIndex] pubKey: pubKey];

// Load the JWS.
CkoStringBuilder *sbJws = [[CkoStringBuilder alloc] init];
[sbJws Append: @"eyJhbGciOiJFUzI1NiJ9"];
[sbJws Append: @"."];
[sbJws Append: @"eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt"];
[sbJws Append: @"cGxlLmNvbS9pc19yb290Ijp0cnVlfQ"];
[sbJws Append: @"."];
[sbJws Append: @"DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA"];
[sbJws Append: @"pmWQxfKTUJqPP3-Kg6NU1Q"];

success = [jws LoadJwsSb: sbJws];
if (success == NO) {
    NSLog(@"%@",jws.LastErrorText);
    return;
}

// Validate the 1st (and only) signature at index 0..
int v = [[jws Validate: [NSNumber numberWithInt: signatureIndex]] intValue];
if (v < 0) {
    // Perhaps Chilkat was not unlocked or the trial expired..
    NSLog(@"%@",@"Method call failed for some other reason.");
    NSLog(@"%@",jws.LastErrorText);
    return;
}

if (v == 0) {
    NSLog(@"%@",@"Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both.");
    return;
}

// If we get here, the signature was validated..
NSLog(@"%@",@"Signature validated.");
NSLog(@"%@",@"--");

// Recover the original content:
NSLog(@"%@",@"Recovered content:");
NSLog(@"%@",[jws GetPayload: @"utf-8"]);
NSLog(@"%@",@"--");

// Examine the protected header:

CkoJsonObject *joseHeader = [[CkoJsonObject alloc] init];
success = [jws GetProtectedH: [NSNumber numberWithInt: signatureIndex] json: joseHeader];
if (success == NO) {
    NSLog(@"%@",jws.LastErrorText);
    return;
}

joseHeader.EmitCompact = NO;

NSLog(@"%@",@"Protected (JOSE) header:");
NSLog(@"%@",[joseHeader Emit]);

// Output:

// 	Signature validated.
// 	--
// 	Recovered content:
// 	{"iss":"joe",
// 	 "exp":1300819380,
// 	 "http://example.com/is_root":true}
// 	--
// 	Protected (JOSE) header:
// 	{ 
// 	  "alg": "ES256"
// 	}